1. Field of the Invention
This invention relates to a display apparatus having a function of vertical smooth scrolling in a part of the area of a CRT screen.
2. Prior Art
Heretofore, a method for displaying different data groups (such as characters) on a plurality of divided areas on the screen in a CRT display device has been known. Japanese Published Unexamined Patent Application No. 54-105435 discloses a display device having a partial vertical scrolling function to shift characters vertically only in specific areas while keeping characters still in other areas. However, the shifting unit on scrolling is a character line, and the smooth scrolling function to shift characters by the unit of dot is not provided.
On the other hand, the display control method disclosed in Japanese Published Unexamined Patent Application No. 49-90459 establishes static and dynamic areas on a screen, and shifts characters by the unit of dot within the dynamic area. The possibility of shifting not only in the horizontal direction but also in the vertical direction is suggested. However, these two types of areas are fixed and cannot be established flexibly, and two separate memories are required to be assigned to the two areas. In Japanese Published Unexamined Patent Application No. 58-207077, a display device for performing the vertical smooth scrolling by sequentially changing the content of a current raster counter to control read out of the character generator is disclosed. However, this device shifts characters in the whole area of the screen, and has no function to shift only characters in a specific area.